Data cartridge carousel

ABSTRACT

A lightweight carousel is disclosed for use in an automatic cartridge library system, featuring a system of guide blocks and springs to hold tape cartridges securely but permit their removal and replacement by bidirectional manipulators. The manipulators carry hinged hooks that can be used to push cartridges radially outward, or upon flexing of the hinges, expand to grip the cartridge for pulling radially inward. A reflective optical sensor is used to confirm that each cartridge in the carousel is properly placed. Optical sensors also verify proper rotation of the carousel, index the carousel, and detect the presence of cartridges in the tape drives. The carousel carries drive pins which seat in tapered holes in an index plate, and is driven by a zero-backlash belt.

This is a continuation, of application Ser. No. 07/984,294, filed 30Nov. 1992, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to the field of automated data storage systems,and in particular to carousel data library systems in which manydiscrete media elements, such as tape cartridges, are stored andmanipulated for access to the information recorded therein.

Tape cartridge libraries are in demand as a means of providingrelatively rapid and automatic access to a large quantity of informationat low cost, while also providing conveniently compact storage. Oneexample of a prior art cartridge library is the IGM-ATL 2300 automatedtape library, sold by IGM Data AutoLoader Division, based in Bellingham,Wash. That system used a carousel to carry up to fifty-four 8 mm tapecartridges, for automatic loading into tape drives, with access to atotal storage volume of up to 270 gigabytes of data. Another exampleprior art system is the STL-8000 8 mm automated tape library, offered bySpectra Logic of Boulder, Colo., using a carousel with space for fortycartridges.

Such prior art systems were not without disadvantages. For example, theweight of the carousel was often excessive for easy handling by humanoperators. In addition, the schemes employed for retaining cartridgeswithin the carousel sometimes proved unsatisfactory in use. In the caseof the ATL-2300, for instance, the carousel had one configuration fortransport and handling, and another for use. In the "secure" mode forhandling, each cartridge was constrained from radial motion out of thecarousel by a metal peg protruding downward from the carousel top at theouter edge, aligned roughly at the middle of the cartridge chamber. Wheninstalled in the library, the carousel was manually shifted to theoperating configuration by rotation of a knob, which angularly displacedthe set of fifty-four pegs so that they were no longer aligned with thechambers, thus permitting the cartridges to move in and out.

If the carousel were removed from the library without first securing thecartridges, the cartridges could slide and fall out of the carouselunintentionally. Furthermore, in operating configuration within thelibrary, the cartridges were not constrained from migrating outward as aresult of vibration and frequent acceleration of the carousel, bringinga risk of jamming of the mechanism. The manually operated peg systemalso added undesired weight to the carousel; the weight of the tapecartridges is significant in itself, and additional structural weight isundesirable.

The configuration of the library also yielded inefficiencies. Forexample, the ATL-2300 cartridges were carried radially in the carousel,and need to be pushed into and out of the carousel for use by tapedrives placed outside the carousel. Motorized pushing shafts were placednear the axis of the carousel to push the cartridges outward toward thetape drives, but separate systems, located outside the carousel by thetape drives, were needed to push them back in again. Additionalcomplexity and costs arise from the extra motors, shafts, and so forthneeded for the separate pushing operations.

In the case of the STL-8000, the tape drives were placed entirely withinthe inner diameter of the carousel. This required placement of eachcartridge at an angle to the carousel, rather than radially, andrestricted the number of cartridges that could be carried while stillfitting within the form factor required for standard cabinet racks.Reduced storage capacity was a result. In addition, placement of thetape drives in the interior of the carousel increases the difficulty ofproviding cooling air to the drives.

Consequently, a need exists for a carousel library system having alightweight carousel that has a simple and automatic scheme forretaining cartridges securely during transport and handling, andretaining them in place during motion of the carousel, but permittingeasy removal by the library mechanism when desired. An ideal systemwould also have provisions for moving cartridges back and forth fromtape drives to the carousel that is simple and robust while employingfewer motors and related hardware. It is also highly desirable tominimize the chance that cartridges will be improperly loaded into thecarousel.

Achieving each of these desired attributes is complicated by the choiceof media. For standard 8 mm data cartridges, the design of the cartridgecase offers few features to be exploited for easy handling or forensuring proper orientation.

SUMMARY OF THE INVENTION

In accordance with the preferred embodiment of the present invention, adata cartridge library system features a lightweight carousel thatretains cartridges through the use of simple wire springs which gripsmall depressions in the cartridges. Each such spring is sufficientlypowerful to retain the cartridge during handling, but may be overcome bythe manipulating apparatus within the library. The springs are mountedon guide blocks, fitted to the top and bottom interior surfaces of thecarousel, which create chambers for the cartridges, while adding minimalweight. Tape drives are placed outside the periphery of the carousel,where the cartridges may be delivered to them by radial motion.

The cartridges may be pushed outward from the carousel to a tape drive,and drawn back into the carousel, by bidirectional manipulatorsoperating from a position within the diameter of the carousel. Themanipulators carry hinged hooks which abut the cartridge during apushing operation, but can be forced over the edges of the cartridge todrop into the depressions in the cartridge sides to grip the cartridgefor pulling it in the opposite direction.

In addition, optical sensing is used to confirm that each cartridge inthe carousel has been properly loaded. Optical sensors also are used toverify that a cartridge is in a tape drive, to index a carousel, and toconfirm proper rotation of the carousel.

The resulting system offers high capacity storage with a maximal numberof cartridges carried in a lightweight carousel, while still fittinginto a standard rack. The carousel holds the cartridges through roughmanual handling, but requires no reconfiguration for use in the library.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an 8 mm tape data cartridge.

FIG. 2 is a perspective view of a carousel.

FIGS. 3A, 3B, and 3C are respectively top, side, and end views of aguide block.

FIG. 4 is a perspective view of a wire spring.

FIGS. 5A and 5B are respectively top and side views of a guide blockfitted with a spring.

FIG. 6 is a top view of a portion of a carousel lower ring fitted withguide blocks.

FIG. 7 is a view from inside a carousel showing a cartridge.

FIG. 8 is a view from outside a carousel showing a cartridge.

FIGS. 9A and 9B are side views of a cartridge, guide block, and spring,showing successive positions of a cartridge.

FIG. 10 is a cross-section view of a carousel.

FIG. 11 is a side view of a cartridge manipulator.

FIG. 12 is an exploded view of the construction of a cartridgemanipulator.

FIGS. 13A, 13B, and 13C are side views of a bidirectional manipulatorrespectively in pushing, transitional, and pulling contact with acartridge.

FIGS. 14A and 14B are side views of a cartridge, guide block, andmanipulator, showing successive positions.

FIG. 15 is a view from inside a carousel along the shaft of amanipulator.

FIG. 16 is a perspective view of a manipulator and its drive system.

FIG. 17 is a diagram of a top view of a cartridge library system, inwhich the carousel is not installed.

FIG. 18 is a side view of the carousel drive of a cartridge librarysystem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention will be described inthe context of a library system for use with standard 8 mm tape datacartridges, although those skilled in the art will recognize that thedisclosed structures are readily adaptable for broader application. Notethat whenever the same reference numeral is repeated with respect todifferent figures, it refers to the corresponding structure in each suchfigure.

Salient features of a standard 8 mm data cartridge can be appreciated byreferring to FIG. 1, in which a data cartridge 10 is depicted. Forconvenience in describing the orientation of cartridge 10, the surfacebearing label 12 will be called the back, while the surface bearingwindow 14 will be called the top. A hinged cover 16 protects the tapepath at the front of the cartridge. Note that cover 16 is tapered towardthe top of cartridge 10. A depression 18 is provided on the right sidenear the back. A similar depression is symmetrically placed on the leftside, but is not visible in this view. The bottom surface of thecartridge is also hidden in this figure; it includes openings over thehubs of the tape reels carried inside cartridge 10. Item 20 on the backsurface is a write-protect tab which may be positioned to permit orprevent recording on the tape. As depicted, cartridge 10 is standing onits left side.

The general configuration of a carousel 22 for carrying multiplecartridges 10 is shown in FIG. 2. Cartridges 10 will be carried betweenlower ring 24 and top 26, oriented with the left side of each cartridgetoward ring 24 and the front of each cartridge facing outward from thecenter of the ring. A set of posts 28 connects ring 24 with top 26 andfixes a uniform spacing between them adequate to hold the cartridges.Around the center of top 26 is a recessed area 30 in which a handle 32is placed to permit easy insertion and removal of the carousel from alibrary system. In the preferred embodiment, carousel 22 includesadditional structure to position and retain the cartridges. The detailsof the that structure will be explained by referring to FIGS. 3A-C.

A guide block 34 is shaped to accommodate cartridges 10. In the top viewof FIG. 3A, cartridge stops 36 are seen at the back end of cartridgesupporting surfaces 38. At the front end of surfaces 38 are ramps 40 toassist in aligning a cartridge as it is placed into the carousel. Acentral spine 42 includes tapered end 44 for the same purpose. Alsovisible in the spine is a hole 46, which serves a dual purpose. It maybe shaped as a hexagonal cavity with a round aperture in the center,suitable for retaining a hex nut for attachment of block 34 to thecarousel. It may also serve as a socket for one of posts 28.

As seen in the side view of FIG. 3B, an alignment pin 48 is alsoprovided for positioning block 34 on the carousel. Block 34 also carrieswedge 50, stop 52, and notch 54; the functions of these features will beexplained in due course. A front end view in FIG. 3C shows pin 48 aswell as ramps 40, tapered end 44 of spine 42, and surfaces 38.

FIG. 4 shows a wire spring 56, having retaining ends 58. In thepreferred embodiment, half of the blocks 34 will be fitted with springs56. Once fitted, the configuration will be as shown in FIGS. 5A-B. Notethat one end of spring 56 fits within notch 54. The sides of the springthen pass over wedges 50 and under stops 52, causing a curvature topreload the spring in the vertical plane. Retaining ends 58 are shownprotruding above surfaces 38 where those surfaces are narrowed towardspine 42.

A set of blocks 34 is mounted on carousel 22 to form chambers forcartridges 10. Pairs of adjacent blocks 34 cooperate to hold a cartridgebetween them. The placement of blocks 34 can be understood by referringto FIG. 6. There, a portion of ring 24 is shown, with three blocks 34attached. A dotted outline 60 indicates the perimeter of a cartridge 10as it would be placed between two of the blocks 34. Since this is a topview, it will be understood that the cartridge is placed on its leftside with its back toward the center of ring 24 and against stops 36,and the tapered front of cartridge toward the outside of ring 24. In thepreferred embodiment, the blocks are positioned radially with respect tothe center of ring 24. As can be seen, the cartridges 10 thus are alsoradially positioned.

Note that the outer two of the three blocks 34 of FIG. 6 are each fittedwith a spring, but that the center block is not so fitted. Normally,blocks with and without springs are alternated around the ring 24. Inthe preferred embodiment, fifty-four blocks will be used on the ring,twenty-seven of them having springs, creating chambers for fifty-fourcartridges.

The arrangement of blocks shown in FIG. 6 is duplicated, with theexception of spring placement, on the lower surface of top 26 ofcarousel 22, to accommodate the right side of each cartridge. Anadditional fifty-four blocks are inverted and attached to the undersideof top 26 to align with the blocks below on ring 24. In the preferredembodiment, however, the location of each of the spring-fitted blocks onthe top is shifted by one position with respect to the blocks on thelower ring. Thus, if a particular block on the lower ring carries aspring, the block immediately above it on the top 26 will not have aspring.

To better understand the reason for this orientation, note that in FIG.6 the spring retaining end 58 within outline 60 is in a position tointeract with the depression 18 that would be found on the left side ofthe cartridge represented by the outline. Furthermore, the springretaining end 58 would rise into the end of that depression 18 closestto the cartridge top surface (that is, toward the bottom of the Figure).Placement of the springs on the blocks attached to the carousel top willpresent a downward extending spring retaining end toward the depressionin the right side of cartridge 10 at the end of the depression closestto the cartridge bottom (that is, toward the top of the Figure). Eachcartridge will then be in contact with two retaining ends 58, one on thecartridge left side and one on the cartridge right side, at diagonallyopposite ends of the depressions 18.

Each cartridge 10 will thus be held in a chamber created by four guideblocks, as shown in FIG. 7. In that view, looking radially outward froma point near recessed area 30 close to the center of carousel 22, theinner ends of four blocks 34 are seen, along with label 12 andwrite-protect tab 20 of cartridge 10. Two blocks 34 are attached to top26 and two are attached to ring 24. Dotted lines have been placed toapproximate the position of spring retaining ends 58, which wouldotherwise not be visible in this view, but which provide the diagonallyopposite contact described above.

A view in the opposite direction is provided in FIG. 8, depicting thesame portion of the carousel as in FIG. 7, but looking radially inwardtoward the center of carousel 22 from a position outside the carousel.The front face cover 16 of cartridge 10 is visible, with the tapering ofthat face toward the right of the Figure. Neighboring blocks formchambers for additional cartridges, not shown. Note that in both FIG. 7and FIG. 8, channels 62 can be seen between blocks 34 and above andbelow cartridge 10, which permit a manipulator to pass through radiallyfor loading and unloading of the carousel.

Once cartridges are loaded, spring 56, through the pressure of retainingends 58, keeps the cartridges secure in the carousel. In practice, ithas been found that cartridges will remain securely in place not onlywhile the carousel is subjected to rotational motion within librarysystem, but also while the carousel is removed from the system duringhandling and transporting by human operators of the equipment. It hasbeen estimated that the cartridges will be retained through 2 g's ofacceleration.

While providing security, the retaining ends 58 are also designed toavoid interference with loading and unloading of the carousel. Thisfeature can be understood by referring in sequence to FIGS. 9A and 9B.In FIG. 9A, a cartridge 10 is being radially inserted into carousel 22from the outside. For clarity of presentation, only a portion cartridge10 and a single spring-fitted block 34 are shown. The cartridge 10 issliding from left to right in the Figure, supported on surface 38. Thecorner of cartridge 10 has forced retaining end 58 downward from theposition depicted in FIG. 5B. Spring 50 has been deflected so that it nolonger contacts stop 52, but is flexed over the fulcrum provided bywedge 50. The position of depression 18 in the left side of thecartridge is indicated by a dotted line.

With the spring so deflected, the cartridge can slide unhindered towardstop 36. As the cartridge 10 reaches stop 36, as shown in FIG. 9B,retaining end 58 slips upward into depression 18 to hold the cartridgesecurely in position. Although not depicted, a corresponding springaction will occur at the diagonally opposite block attached to the topof the carousel.

When removal of a cartridge is desired, the spring force may be overcomeby pushing outward on the cartridge. In that case, the action will berepresented by referring first to FIG. 9B, and then to FIG. 9A, andassuming motion of the cartridge in the opposite direction from thatdiscussed above.

The construction of a complete carousel is represented in thecross-section view of FIG. 10. Ring 24 and top 26 each carry blocks 34,half of which are fitted with springs 56. Posts 28 are used to connectthe ring and the top. In the preferred embodiment, it has been foundthat placement of a post in every sixth block provides adequate rigiditywithout unduly increasing the weight of the carousel.

Handle 32 lies within recessed area 30. Extending below that recessedarea are drive pins 64. In the preferred embodiment, four such drivepins are used. These pins serve to establish the center of rotation ofthe carousel, to provide alignment of the carousel, and to transmitdriving torque.

A shutter plate 66 protrudes below recessed area 30. This plate carriesa rim intended to interact with an optical sensing device. For example,a large notch 68 may be provided to permit sensing of an initial orindexed position for the carousel. As the edge of the notch passes anoptical sensor, the rotational position of the carousel can bedetermined. In addition, evenly spaced slits 70 may also be provided. Byusing an optical sensor to count passage of such slits, the librarysystem can verify that the actual angle of rotation of the carouselmatches that which was desired, to permit detection of drive systemfailures.

The guide blocks 34 may be constructed of teflon fiber impregnatedpolycarbonate. It has been found that such material provides goodfrictional behavior with typical cartridges. The top and ring may bethin formed aluminum. The resulting structure is so light that theentire carousel weighs only about ten pounds when fully loaded withfifty-four cartridges.

A bidirectional cartridge manipulator 72 suitable for use with carousel22 is shown in FIG. 11. A shaft 74, carrying gear teeth rack 76, isattached to a cross-member 78. At each end of the cross-member is ahinge 80, which carries a triangular cross-section hook 82. Hinges 80are spring biased toward each other by springs 84. Screws 86 provideadjustable stops for the motion of the hinges 80.

Construction of manipulator 72 in the preferred embodiment is furtherillustrated in FIG. 12. Pins 88 are used to fix the components together.Cross-member 78, shaft 74, and hinges 80 are preferably metal, but hooks82 are formed of plastic.

Operation of the manipulator 72 is shown in FIGS. 13A-C. In FIG. 13A,manipulator 72 is shown in contact with cartridge 10, as it would bealigned for pushing the cartridge out of the carousel from behind. Notethat hooks 82 contact the back of the cartridge on the outer slopingsurfaces of the hooks. The strength of the springs 84 and the slope ofthe outer surface of the hooks are chosen so that hinges 80 will notflex outward under the normal frictional resistance of a cartridgesliding on blocks 34, and so that spring retaining ends 58 will yieldbefore the springs 84. Thus, the cartridge can be freed from retainingends 58 and slide out of the blocks 34 under the force applied bymanipulator 72, while the cartridge remains in contact with only theouter edges of hooks 82. Such a pushing operation would ordinarily beused, for example, to feed a cartridge to a tape drive for a reading orwriting operation. The manipulator is driven a known distance, at whichpoint the cartridge is grasped by the mounting mechanism of the tapedrive, and the manipulator may be withdrawn.

To retrieve a cartridge from a tape drive and replace it in thecarousel, the cartridge must be pulled inward toward the center of thecarousel. This may be accomplished using the same manipulator. Once thetape drive has completed its dismounting operation and returned the tapeto the vicinity of the carousel, the manipulator 72 is once again drivenout to the same known distance as described before, so that the contactbetween the manipulator and the cartridge is once more as shown in FIG.13A.

However, with the cartridge held by the tape drive to resist furtherpushing, the manipulator is driven still farther toward the cartridge.As shown in FIG. 13B, the resistance of the cartridge to pushing motioncauses springs 84 to stretch, hinges 80 to flex outward, and hooks 82 toride over the left and right sides of the cartridge at this transitionalstage. As the manipulator continues to travel, hooks 82 find depressions18 in the sides of the cartridge, and drop into them, as shown in FIG.13C.

The cartridge is now gripped by the manipulator such that it can bepulled from the tape drive back into its proper chamber in the carousel.Interaction of the manipulator with the carousel structure is shown inFIGS. 14A and 14B. As the cartridge 10 is pulled toward the center ofthe carousel on block 34, hook 82 is engaged with depression 18. Therelative strength of springs 84 and 56 and the slope of the inner faceon hook 82 are chosen such that retaining end 58 is forced downward withthe cartridge sliding over it, without flexing hinge 80.

As shown in FIG. 14B, when the cartridge 10 reaches stop 36, continuedtravel of manipulator 72 causes spring 84 to stretch, hinge 80 to flex,and hook 82 to leave depression 18. Meanwhile, retaining end 58 hasflexed upward to reestablish its grip on the cartridge.

Hook 82 is sufficiently narrow that it will not interfere with retainingend 58 in depression 18. This geometry can be better appreciated byreferring to FIG. 15, viewing the cartridge from behind, along the shaft74 of the manipulator. Once again, as in FIG. 7, dotted lines are usedto indicate the positions of retaining ends 58, otherwise not visible inthis view. Note that the hinges and hooks of manipulator 72 fit withinchannels 62 between blocks 34. Furthermore, retaining ends 58 lieoutside the width of hooks 82 on the manipulator, so that the engagementand disengagement of the retaining ends and the hooks with the cartridgeare independent and non-interfering.

The drive mechanism for manipulator 72 is depicted in FIG. 16. Mountingfixture 90 and bushings 92 provide guidance for the shaft 74. As can beseen, fixture 90 also supports motor 94. A gear 96 on the motor forms arack and pinion with the teeth cut into shaft 74. It has been found thatno additional structure is necessary to constrain rotation of shaft 74about its axis, permitting a simple system to be used. Motor 94 ispreferably a stepper motor for precise control of the manipulatorposition. The mounting fixture 90 may be fitted with limit switches,particularly for detecting full retraction, for additional informationon the manipulator position.

The positioning of the manipulator systems with respect to the othercomponents of a library system can be understood by referring to FIG.17.

In FIG. 17, a cartridge library system includes two tape drive units 98,as seen from above. In the preferred embodiment, these are conventional8 mm tape drives such as those marketed by Exabyte Corporation ofBoulder, Colo. Each drive is fitted with a small stepper motor (notshown) to power the tape drive tray for mounting and dismounting thecartridge after delivery from or prior to returning to the carousel. Themotor is modified so that it can be rotated and clamped, so that thetray may be held firmly in position when specific motor phases areenergized. This provides the ability to resist pushing motion by themanipulator, as described above.

An indexing plate 100 carries a set of holes 102 for receiving drivepins 64 of carousel 22. Eighteen such holes are provided in thepreferred embodiment, and each has a large outer opening to assist ineasily seating the carousel. Driving force for the carousel is providedby motor 104 acting through belt 106. Although no carousel is mounted inthis view, a dotted line 108 has been included to show the approximateouter diameter of the carousel in the mounted position. A guide ring 110aids in fitting the carousel in the proper position.

Three manipulator mounting fixtures 90 are visible, each with a motor94. Two are aligned so that cartridges may be pushed toward and pulledfrom drives 98. The third is aligned with an express port 112, explainedmore fully in my copending application of even date entitled "ExpressPort for Cartridge Carousel System."

An optical sensor 114 is provided on one of the manipulator mountingfixtures, for detecting passage of openings in shutter plate 66.Additional optical sensors 116 are placed at the drives 98 to detect thepresence of a cartridge.

A reflective sensor 118 is shown between the two drives. This sensor maybe used to determine whether cartridges are properly loaded; improperloading will prevent a cartridge from being accepted by the tape drives.Since each properly loaded cartridge has a tapered cover 16 which facesoutward from the carousel and to the left as viewed from above, rotationpast the reflective sensor will produce a characteristic signal pattern.The sloping tapered surface will not reflect light back to the sensor asthat edge of the cartridge passes, but the remainder of the frontsurface will so reflect. The sequence of reflections as a function ofthe rotational position of the carousel thus allows the system toconfirm that cartridges have not been loaded with the wrong orientation.

A bar code reader 120 may also be included, positioned so that bar codedlabels on the back of the cartridges will pass before it.

The configuration illustrated permits the entire library system to beconstructed to fit within a standard rack width, while still permittingfifty-four cartridges to be carried within each carousel. Thebidirectional manipulators are mounted on the interior of the carousel,while the tape drives are placed outside of it. Simple radial motion canbe used for delivering tapes to the drives, and the drives arepositioned where cooling air is easily circulated. In normal use, a setof shrouds and covers, not shown, is employed to protect the equipmentand human operators from the dangers each presents to the other.

Referring now to FIG. 18, a side view of the carousel drive systemreveals a spindle 122. Index plate 100 is mounted on the shaftprotruding from the spindle. Holes 102 are represented with dottedlines, so that their interior contour can be appreciated as an aid toplacement the drive pins of the carousel.

Index plate 100 is carried on a hub 124 having sprocket teeth. Theseteeth engage belt 106, which is preferably a positive drivezero-backlash molded polyurethane belt with steel cables, driven bymotor 104. Index plate 100 is adjusted in assembly to have a knownposition with respect to baseplate 126 when specific phases of steppermotor 104 are energized, so that the angular position of the carouselrelative to the baseplate is accurately established whenever aparticular phase is energized.

One manipulator mounting fixture 90 is also visible in FIG. 18. At thetop of fixture 90 is guide ring 110, and on another upper surface isoptical sensor 114. A manipulator shaft 74 protrudes toward the spindle.The dimensions of the system are chosen so that sufficient outwardtravel of the manipulator can be had to deliver cartridges to tapedrives, yet the fully retracted manipulator still fits completely withinthe inner radius of lower ring 24 of the carousel without running afoulof spindle 122. In this view, the manipulator is not shown fullyretracted, but is positioned so that hooks 82 are just protruding to theleft of the Figure, so that the reader may better visualize the relativeplacement of the components.

I claim:
 1. A carousel for use in an automated library system, adaptedto carry a plurality of data cartridges, each data cartridge havingpreformed depressions on two opposite faces, comprising:a top memberhaving a substantially circular periphery; a lower member having asubstantially circular periphery; spacing means, for holding the lowermember at a fixed distance from the upper member and with the centers ofthe top member and of the lower member on a common central axis; aplurality of cartridge guides affixed to the top member; a plurality ofcartridge guides affixed to the lower member, adjacent pairs of thecartridge guides on the lower member being disposed to retain betweeneach pair one of the data cartridges in a radial orientation withrespect to the central axis; and a plurality of spring means, attachedto selected ones of the cartridge guides, for engaging depressions onthe data cartridges faces to provide a retaining force againstinadvertent displacement of a cartridge from the carousel, each springmeans including a wire spring, attached to one of the cartridge guidesand preloaded to exert a force in a direction parallel to the centralaxis.
 2. A carousel as in claim 1, wherein for each adjacent pair ofcartridge guides affixed to the lower member only one of the cartridgeguides of that pair has one of the spring means attached.
 3. A carouselas in claim 2, wherein:each of the cartridge guides affixed to the topmember is aligned above one of the cartridge guides affixed to the lowermember; and for each cartridge guide affixed to the lower member thathas one of the spring means attached, the cartridge guide affixed to thetop member and aligned above it does not have a spring means attached.4. A carousel as in claim 1, wherein the wire spring includes aretaining end shaped to engage one of the depressions in one of the datacartridge faces.
 5. A carousel as in claim 4, wherein the retaining endof the wire spring is free to flex away from the depression in the datacartridge face in response to forced displacement of the data cartridgein a radial direction with respect to the central axis.
 6. A carousel asin claim 1, further comprising shutter means for cooperation with anoptical sensor in the automated library system, to provide signalsindicative of the rotational position of the carousel with respect tothe central axis,
 7. A carousel as in claim 1, further comprising aplurality of drive pins, extending beneath the top member and disposedabout the central axis for transmitting driving torque to the carousel.8. A carousel as in claim 1, wherein each cartridge guide includes acartridge supporting surface, the cartridge supporting surface of eachcartridge guide attached to the lower member being displaced above thelower member, and the cartridge supporting surface of each cartridgeguide affixed to the top member being displaced below the top member. 9.A carousel as in claim 8, wherein the cartridge supporting surfaces ofadjacent pairs of cartridge guides attached to the lower member arespaced apart to provide a channel for passage of a cartridgemanipulator.